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TMS320F28377D-EP: Crystal Frequency

Kevin Bachovchin
Prodigy 70 points
Part Number: TMS320F28377D-EP
Other Parts Discussed in Thread: C2000WARE

Hello,

I see on the datasheet that the maximum SYSCLK TMS320F28377D-EP is 200 MHz.  The datasheet also lists the frequency range for the external crystal as 10 - 20 MHz.  Does the frequency of the external crystal have any effect on how fast code can execute, or that entirely determined by SYSCLK?  For example, would using a 20 MHz crystal instead of a 10 MHz make the same code execute faster?

Thanks,

Kevin

  • +1
    TI__Guru 74290 points

    Kevin,

    We have an on-chip PLL that is used to scale up the frequency provided from the external clock.  In our SW example in C2000Ware you will see there is an assumed clock rate and the PLL will use the correct multipliers to get 200MHz.

    From a bare silicon POV, if in your code you never enabled the PLL, then yes you would see faster code execution with 20MHz vs 10MHz, but practically in either case you would use the PLL to scale to 200MHz for either clock (or something in between) so the code execution would then be the same.

    The DS range is just to provide what ranges we support for the external clock, if you have a preferred X-tal within that range you can scale the PLL multipliers accordingly.  One last point is that the PLL multipliers are integer based, so while both 10MHz/20MHz can get 200MHz, if you picked something that is not an integer multiple of 200MHz, then the final sysclk would end up being below 200MHz, by whatever integer ratio is available.

    Best,

    Matthew